Summary In the United States, perinatal brain injury (PBI) is a major cause of infant mortality and long-term disability in children. For a large proportion of infants with PBI, central nervous system (CNS) injury begins in utero with inflammation (chorioamnionitis/CHORIO) and/or hypoxia-ischemia. CHORIO contributes to preterm CNS injury, and is also a common, independent risk factor for brain injury in term infants, including perinatal stroke. However, the molecular mechanisms mediating inflammation in the placenta-fetal-brain axis that cause PBI remains a gap in knowledge. The chemokine (C-X-C motif) ligand 1 (CXCL1) and its receptor (CXCR2) have been clinically implicated in CHORIO, and are essential to neutrophil recruitment, neural cell development and adult CNS injury, although their specific role in PBI pathophysiology is completely undefined. We propose to use our established and unique model of CNS injury associated with CHORIO to delineate how in utero inflammation precipitates PBI. Our central hypothesis is that CXCL1 secreted by the choriodecidua during CHORIO enters fetal blood, transcends the placenta-fetus-fetal brain axis, and through interactions on CXCR2+ neural cells and neutrophil recruitment, confers injury in the developing CNS. We posit that CHORIO is defined by excess CXCL1/CXCR2 signaling, which is toxic to neural cells over an extended neurodevelopmental period. To investigate this hypothesis we will: 1) Test that CHORIO disturbs CXCL1/CXCR2 signaling throughout the placenta-fetus-fetal brain axis during a critical period of late gestation CNS development; 2) Test that placental CXCL1 translocates to the fetal brain and modulates neutrophils and microglia; and 3) Test that attenuation of CXCL1/CXCR2 signal transduction protects neural cells following CHORIO. Using multiplex electrochemiluminescent immunoassay (MECI), flow cytometry (FC), and qPCR we will investigate whether CHORIO induced CXCL1/CXCL2 signaling is a unifying inflammatory signal transduction mechanism through the placenta-fetus-fetal brain axis. Using in vitro assays, including exosome analyses, placental explants and acute brain slices, we will drive CXCL1/CXCR2, and define the major molecular mediators of damage to the placenta-fetus-fetal brain axis. Using immunoneutralization, microRNA, pharmacological (SB225002), and genetic (CXCR2 KO) approaches, we will delineate whether CXCL1/CXCR2 is necessary and sufficient for immune cell recruitment to the CNS following CHORIO. We predict creating a transient CXCR2 deficiency following CHORIO will attenuate microglial activation and neutrophil recruitment, mitigate white matter and neuronal injury, and improve microstructural coherence on magnetic resonance imaging. These investigations will be the first to connect aberrant CXCL1/CXCR2 signaling in the placenta- fetal-brain axis to chronic injury and impaired neurodevelopment, and will define novel targets for directed therapies for infants at high risk for PBI.